This invention relates to carcass structures for pneumatic tires, particularly bias ply tires, and tires containing said carcass structures.
Bias ply (also called diagonal ply or cross ply) tires have a carcass formed of layers or plies of cord fabric. The reinforcing cords of each layer extend diagonally across the tire from bead to bead. The bias angle of the cord path relative to the axial direction of the tire (i.e. parallel to the axis of rotation of the tire) is greater than 15 degrees. The cords in known types run in opposite directions in each successive layer (or ply) of reinforcing material, resulting in a criss-cross pattern. Normally, an even number of layers is employed. To further reinforce the tire, additional layers of reinforcing material or plies may be included, these layers overlying the crown area of the tire to further reinforce the tread region. These layers are called "breakers" and the cords of these reinforcements do not extend to the bead portions of the tire.
Wherever herein, the term "bias" or "bias ply tire" is employed, it shall mean a tire in which a majority of the reinforcement of the tire is obtained by bias plies. The contribution of each layer of reinforcements is calculated by taking the number of cords per inch in the cured tire (measured perpendicularly to the longitudinal axis of the cords) times the strength per cord times the number of layers. This computation is done with respect to the cord arrangement at substantially the circumferential centerline of the cured tire.
A second type of tire construction is the radial tire. In a radial tire one or more plies of reinforcing cords extend transversely or approximately transversely from bead portion to bead portion. Radially outward of the ply or plies under the tread is an inextensible belt composed of one or more layers of cords, the angles of the belt cords being relatively low, for example, 10 to 30 degrees with respect to the circumferential direction of the tire. These belts act to restrict the axially directed carcass ply cords. The present invention is not directed to tires of the radial type.
As previously stated, when additional strength is required in the crown area of bias tires, additional cord fabric layers (breakers) are laid over the plies whose cords extend from bead portion to bead portion. Application of these layers involves additional labor and time at the building station, thereby reducing productivity and increasing the cost of such tires. Furthermore, because the cords of such additional layers (breakers) are not restrained by the beads of the tire, the cords of these breakers are free to move upon shaping of the tire from a cylindrical form to its completed form. Such movement, when irregular, may result in a defective tire.
It is, therefore, an object of this invention to provide a bias ply vehicle tire which will overcome the above-mentioned drawbacks.
It is another object of this invention to provide a bias ply pneumatic tire containing additional layers of reinforcing cords in its crown area without requiring the separate addition of such reinforcement layers at the building machine.
It is a still further object of this invention to provide a bias ply pneumatic vehicle tire in which the reinforcing cords of the additional layers in the crown area thereof are anchored near the bead portions of the tire thereby reducing or eliminating movement of the cords thereof during shaping of the tire.
Other objects will become apparent as the description proceeds.